This invention relates in general to a method of converting a gray scale pixel image to a binary pixel image. More particularly, it relates to an efficient method of obtaining an improved final binary pixel image of a fingerprint from a gray scale pixel image.
U.S. Pat. No. 4,322,163 issued on Mar. 30, l982 describes the optical and mechanical components of a finger indentification system. As described therein, an optical scan of a subject finger placed against a platen provides a modulated relected light beam that is imaged at or near an array of photoelectric detectors.
The disclosure of the referenced patent is incorporated herein for the purpose of simplifying the description.
In order to process a fingerprint image in automatic processing equipment, the image must be such that each pixel has a binary value, one of which is a "white" or "one" value representing a ridge and the other of which is a "black" or "zero" value representing a valley. In order to have a reliable, useful access control or identification system, the binary fingerprint image obtained from the gray scale image must accurately reflect the ridges and valleys of the fingerprint itself. To obtain such an accurate image one must insure that the original fingerprint image is accurately converted to a gray scale image and that this gray scale image is accurately converted to a binary image. In addition to accuracy, the method for converting must be relatively inexpensive and quick. Clearly, the more accurate the binary image is the more reliable and useful will be either the access or the identification system.
Accordingly, it is a purpose of this invention to provide an improved method of accurately converting a gray scale image of a fingerprint to a binary image of the fingerprint.
It is a further purpose of this invention to provide such a method which is relatively inexpensive and which works quickly and efficiently.